If you need to correct or change your return after it has been filed, but before the automatic extension due date has passed, you must file a corrected
IL-1120-ST-X, Amended Small Business Corporation Replacement Tax Return. Mark the form "CORRECTED" at the top and show the changes. Any correction made may cause a recalculation of penalties and interest. If you need to correct or change your return after it has been filed, and the automatic extension due date has passed, you must file
Form IL-1120-ST-X showing the changes. For more information refer to
IL-1120-ST-X Instructions.
